Image forming apparatus

ABSTRACT

An image forming apparatus includes a stacking unit having a stack tray, a conveyance unit, an image forming unit, a direct current (DC) brush motor, a drive unit, a detector, a first determiner, and a second determiner. An image forming unit forms an image on a sheet conveyed by the conveyance unit from the stack tray. The drive unit drives the DC brush motor to lift and lower the stack tray in a vertical direction. The detector detects a drive current flowing through a DC brush motor winding. The first determiner determines a DC brush motor rotor rotation amount based on the number of times an absolute value of a current value of the detected drive current changes from a value smaller than a threshold to a value greater than the threshold. The second determiner determines a residual amount of stack tray stacked sheets based on the determined rotation amount.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to detection of a residual amount of sheets in an image forming apparatus.

Description of the Related Art

Conventionally, there has been known a method for detecting a residual amount of sheets stacked in a cassette provided in an image forming apparatus. For example, Japanese Patent Application Laid-Open No. 1-231735 discusses a copy machine that detects a residual amount of sheets based on an electric current flowing through a winding of a motor that drives a lift table for lifting and lowering sheets stacked in a cassette. A value of the electric current flowing through the winding of the motor corresponds to a load torque applied to the motor.

A weight of each sheet varies depending on a type of the sheet. For example, a load torque applied to the motor in a case where a first number of thick papers is stacked in a sheet feed cassette is greater than a load torque applied to the motor in a case where the first number of thin papers is stacked in the sheet feed cassette. That is, in a configuration discussed in Japanese Patent Application Laid-Open No. 1-231735, a value of the load torque applied to the motor varies depending on the type of sheet to be stacked, so that it is difficult to detect the residual amount of sheets stacked in the sheet feed cassette with high accuracy.

SUMMARY OF THE INVENTION

The present disclosure is directed to an image forming apparatus that detects a residual amount of sheets with higher accuracy.

According to an aspect of the present disclosure, an image forming apparatus includes a stacking unit including a stack tray on which a sheet is to be stacked, a conveyance unit configured to convey the sheet stacked on the stack tray, an image forming unit configured to form an image on the sheet conveyed by the conveyance unit, a direct current (DC) brush motor configured to lift and lower the stack tray in a vertical direction, a drive unit configured to drive the DC brush motor, a first detector configured to detect a drive current flowing through a winding of the DC brush motor, a first determiner configured to determine a rotation amount of a rotor of the DC brush motor based on the number of times an absolute value of a current value of the drive current detected by the first detector changes from a value smaller than a threshold to a value greater than the threshold, and a second determiner configured to determine a residual amount of sheets stacked on the stack tray based on the rotation amount determined by the first determiner.

Further features of the present disclosure will become apparent from the following description of embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an image foxing apparatus.

FIG. 2 is a control block diagram of the image forming apparatus.

FIG. 3 is a view illustrating a structure of a geared motor.

FIG. 4 is a view illustrating a structure of a direct current (DC) brush motor.

FIG. 5 is a diagram illustrating a relationship between a rotation of a motor and a current waveform.

FIG. 6 is a table indicating a relationship between an accumulated count value and a residual amount of sheets.

FIG. 7 is a control block diagram of a lifter control unit.

FIG. 8 is a diagram illustrating a signal before and after processing by a filter unit.

FIG. 9 is a flowchart for determining a residual amount of sheets when a power source is turned on.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

The following embodiments are not intended to limit the claimed disclosure. In addition, not all features described in the following embodiments are necessarily essential as a solution for the present disclosure.

<Image Forming Apparatus>

FIG. 1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus 100 according to the present embodiment.

The image forming apparatus 100 includes a document feeding device 201, an image reading device 202, and an image printing device 300.

Hereinafter, the configuration of the image forming apparatus 100 will be described in conjunction with operations thereof.

Documents P stacked on a document stacking unit 203 of the document feeding device 201 are fed one by one by a pickup roller 204 and conveyed to a reading position by conveyance rollers 207 and 208, and the like.

The document P is conveyed to pass over an image reading optical system 209 of the image reading device 202 at a constant speed. Then, after an image is read by the image reading device 202, the document P is discharged out of the device by a discharge roller 210.

Meanwhile, reflected light of the image on the document P illuminated by an illumination system 211 at the reading position of the image reading device 202 is guided to an image reading unit 215 by an optical system including reflection mirrors 212, 213, and 214, and is converted into an image signal in the image reading unit 215. The image reading unit 215 includes a lens, a charge coupled device (CCD) as a photoelectric conversion element, and a drive circuit for the CCD.

A document reading mode includes a first reading mode and a second reading mode.

In the first reading mode, the image on the document P is read while the document P is conveyed at a constant speed in a state where the image reading optical system 209 is stopped.

On the other hand, in the second reading mode, the image on the document P placed on a document glass table 216 of the image reading device 202 is read while the image reading optical system 209 is moved at a constant speed.

A sheet-like document is normally read in the first reading mode. A bound document is normally read in the second reading mode.

The image signal obtained by the conversion in the image reading unit 215 is transmitted to the image printing device 300.

A laser beam modulated based on the image signal passes through an optical scanning device 311 including a polygon mirror, and mirrors 312 and 313, and is exposed on a photosensitive drum 309. A surface of the photosensitive drum 309 is uniformly charged by a charging unit 310, and by irradiation of an outer peripheral surface of the photosensitive drum 309 with the laser beam, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 309. The electrostatic latent image is developed by toner stored in a developer unit 314, and a toner image is transferred to a sheet by a transfer separation unit 315.

A sheet feed cassette 401 can be inserted into and pulled out from the image printing device 300. A sheet is stacked on an intermediate plate 405 in the sheet feed cassette 401 in a state where the sheet feed cassette 401 is pulled out.

An opening/closing state of the sheet feed cassette 401 is detected by a sheet feed cassette open/close sensor 407 placed on a side of the sheet feed cassette 401 in the image printing device 300.

When the sheet feed cassette 401 is inserted into the image printing device 300, a gear 402 placed on a side of the sheet feed cassette 401 is connected to a geared motor 404 that lifts and lowers the intermediate plate 405 in a vertical direction.

When the insertion of the sheet feed cassette 401 into the image printing device 300 is detected by the sheet feed cassette open/close sensor 407, driving of the geared motor 404 is started.

The image printing device 300 is provided with a sheet height sensor 406 that detects an uppermost surface of sheets.

The intermediate plate 405 is lifted by the geared motor 404 until the sheet height sensor 406 detects the uppermost surface of the sheets.

When the sheet feed cassette 401 is pulled out from the image printing device 300, the gear 402 placed on the side of the sheet feed cassette 401 and the geared motor 404 are disconnected. As a result, the intermediate plate 405 in the sheet feed cassette 401 is lowered to move to a reference position as a bottom position of the sheet feed cassette 401.

A configuration and an operation of a sheet feed cassette 501 are similar to those of the sheet feed cassette 401. Hereinafter, with respect to common portions between the sheet feed cassette 401 and the sheet feed cassette 501, description will be made using the sheet feed cassette 401.

The sheet stacked in the sheet feed cassette 401 is conveyed by a pickup roller 403 and a conveyance roller 306 to a registration roller 308.

The sheet stacked in the sheet feed cassette 501 is conveyed by a pickup roller 503, the conveyance roller 306, and a conveyance roller 307 to the registration roller 308.

The registration roller 308 feeds the sheet to a position (transfer position) where the transfer separation unit 315 transfers the toner image at a timing when the toner image is to be transferred to the sheet by the transfer separation unit 315.

The sheet to which the toner image has been transferred is conveyed to a fixing unit 318 by a conveyance belt 317. Then, toner on the sheet is fixed to the sheet by the fixing unit 318.

In a case where a one-side printing mode is set, the sheet having passed through the fixing unit 318 is discharged out of the device by a fixing discharge roller 319 and a discharge roller 324.

On the other hand, when a double sided printing mode is set, the sheet passes through the fixing discharge roller 319 and a conveyance roller 320, and conveyed to a reverse path 325 by a reverse roller 321. Further, rotation of the reverse roller 321 is reversed immediately after a rear end of the sheet passes a point where the reverse path 325 and a double-sided path 326 are joined, whereby the sheet is reversed and conveyed to the double-sided path 326. Then, the sheet conveyed to the double-sided path 326 is conveyed by conveyance rollers 322 and 323, and again passes through the conveyance roller 306, whereby an image is formed on a second surface of the sheet by the above-described method.

FIG. 2 is a block diagram illustrating a configuration example of a control system of the image forming apparatus 100.

A system controller 101 includes a central processing unit (CPU) 102, a read-only memory (ROM) 103, and a random-access memory (RAM) 104, and entirely controls the image forming apparatus 100, Units in the image printing device 300 controlled by the system controller 101 include an image processing unit 10, an operation unit 105, an analog-to-digital (A/D) conversion unit 110, a high voltage control unit 111, a motor control unit 112, a lifter control unit 113, sensors 114, and an alternating current (AC) driver 115. The system controller 101 can transmit and receive data to and from each of the above-described units connected thereto.

The CPU 102 in the system controller 101 executes various sequences related to predetermined image forming processing by reading out various programs stored in the ROM 103.

The RAM 104 is a volatile storage device and is used as a work area for the CPU 102 to execute various programs and as a temporary storage area for temporarily storing various data.

The ROM 103 stores data such as a set value for the high voltage control unit 111, a command signal for the motor control unit 112, a size and a residual amount of sheets in the sheet feed cassette 401, and information received from the operation unit 105.

The image processing unit 10 performs image processing based on set value data of each device in the image printing device 300. The set value data is necessary for image processing of data input from the system controller 101.

The system controller 101 displays, on a display unit provided in the operation unit 105, an operation screen for a user to perform various settings. In addition, the system controller 101 receives various set values by the user (for example, a set value of copy magnification and a set value of density) via the operation unit 105.

Further, the system controller 101 transmits data for informing the user of a state of the image forming apparatus 100 to the operation unit 105, The operation unit 105 then displays, on the display unit, information indicating the state of the image forming apparatus 100 (for example, the number of sheets on which an image has been formed, information indicating whether or not an image is being formed, and information indicating occurrence of a jam and a location where the jam occurs) based on the data received from the system controller 101.

The A/D conversion unit 110 receives a detection signal from a thermistor 120 that detects a temperature of a fixing heater 125. In addition, the r-VD conversion unit 110 converts the received detection signal into a digital signal, and sends the digital signal to the system controller 101.

The high voltage control unit 111 supplies a voltage necessary for operations to each of a primary charging unit, a development device, and a transfer device, which are constituting a high voltage unit 121. The set value input from the system controller 101 is generated based on signals from the sensors 114 based on the set value input from the system controller 101.

The motor control unit 112 performs drive control of a motor 122 based on a command signal input from the system controller 101. Although only one motor controlled by the motor control unit 112 is illustrated in FIG. 2 for convenience of description, the number of motors is not limited to one in practice, and a plurality of motors is drive-controlled by the motor control unit 112. In addition, the motor 122 includes not only a motor that drives a roller for conveying a sheet but also motor that drives a fixing roller, a drum, or the like.

The lifter control unit 113 controls a direct current (DC) brush motor 600 (described below with reference to FIG. 3) included in the geared motor 404 based on a command signal input from the system controller 101, to perform a lift-up operation of the sheet feed cassette 401.

The command signal input from the system controller 101 is generated based on the signals from the sensors 114 such as the sheet height sensor 406.

The AC driver 115 controls the fixing heater 125 to a predetermined or desired temperature for fixing processing, based on a control signal generated by the system controller 101 based on the digital signal received from the A/D conversion unit 110. The fixing heater 125 is a heater used for the fixing processing, and is placed in the fixing unit 318,

FIG. 3 is a view illustrating a structure of the geared motor 404 according to the present embodiment.

The geared motor 404 is configured by connecting the DC brush motor 600, which is small in size, and a plurality of gears 601 to 605. By increasing an overall deceleration ratio from the DC brush motor 600 to the gear 605, which is in the final stage, it is possible to cope with lift-up of various sheets having different sizes and basis weights, even when the small-sized DC brush motor 600 is used.

In the present embodiment, as an example, a deceleration ratio between the DC brush motor 600 and the final-stage gear 605 is set to 1000, That is, when the DC brush motor 600 makes 1000 rotations, the final-stage gear 605 makes one rotation.

In addition, the gear 402 placed on the side of the sheet feed cassette 401 rotates in conjunction with the rotation of the final-stage gear 605, and the intermediate plate 405 in the sheet feed cassette 401 is lifted from the reference position as the bottom position.

A structure and an operation principle of the DC brush motor 600 according to the present embodiment will be described,

FIG. 4 is a view illustrating the structure of the DC brush motor 600.

The DC brush motor 600 includes a permanent magnet 701 (701A and 701B), a coil 702, a rotor 703, a commutator 704, and a brush 705 (705A and 705B).

The permanent magnets 701A and 701B serve as stators.

The coil 702 is wound around the rotor 703, and a rotational force is generated by an electric current supplied to the coil 702.

The commutator 704 is provided to a rotation shaft of the rotor 703, and supplies the coil 702 with an electric current supplied from the brushes 705A and 705B in sliding contact with the commutator 704. The commutator 704 is divided into three parts, and the three parts are electrically insulated from each other.

In a case where the rotor 703 rotates by 60 degrees, connection between the commutator 704 divided into the three parts and the brushes 705A and 705B is switched. As a result, a direction of the electric current flowing through the coil 702 is switched, and suction and repulsion are repeated between the rotor 703 and the permanent magnets 701A and 701B, whereby the rotor 703 rotates. When the connection between the commutator 704 divided into the three parts and the brushes 705A and 705B is switched six times, the rotor 703 rotates once.

FIG. 5 is a diagram illustrating a relationship between a signal generated by the rotation of the rotor 703 (motor rotation signal) and a waveform of the electric current flowing through the coil 702 (motor current waveform), when the DC brush motor 600 is rotationally driven.

As illustrated in FIG. 5, the electric current abruptly changes at the timing when the connection between the commutator 704 divided into the three parts and the brush 705 is switched (spike current). That is, switching of electrodes of the commutator 704 connected to the brush 705 can be detected by detection of the spike current.

In the present embodiment, when the connection between the commutator 704 and the brush 705 of the DC brush motor 600 is switched 6000 times, the intermediate plate 405 on which no sheet is stacked moves from the reference position as the bottom position of the sheet feed cassette 401 to a position where the intermediate plate 405 is detected by the sheet height sensor 406.

A method for detecting the residual amount of sheets in the sheet feed cassette according to the present embodiment will be described.

FIG. 6 is a table (T) indicating a relationship between an accumulated count value of the switching of the connection between the brush 705 and the commutator 704 of the DC brush motor 600 and the residual amount of sheets.

When the sheet feed cassette 401 is inserted into the image printing device 300 and detected by the sheet feed cassette open/close sensor 407, the system controller 101 starts lift-up control of the intermediate plate 405 in the sheet feed cassette 401. As the intermediate plate 405 is lifted, the rotor 703 rotates and the connection between the brush 705 and the commutator 704 is switched, A rotation amount of the DC brush motor 600 is calculated by counting of the number of tunes of switching.

The system controller 101 counts the number of times the connection between the brush 705 and the commutator 704 is switched, and stores a count value in the RAM 104.

The system controller 101 then determines the residual amount of sheets based on the table T stored in the ROM 103 and the count value stored in the RAM 104, and displays a determination result on the operation unit 105.

In the present embodiment, the count value stored in the RAM 104 is reset in a case where the sheet feed cassette 401 is pulled out from the image printing device 300, or in a case where the sheet height sensor 406 is turned off when the power source of the image printing device 300 is switched from an OFF state to an ON state.

The lift-up control of the intermediate plate 405 during execution of a print job is performed based on a signal output from the sheet height sensor 406, When the sheet height sensor 406 is turned off, driving of the DC brush motor 600 starts, and when the sheet height sensor 406 is turned on, driving of the DC brush motor 600 stops.

While the DC brush motor 600 is driven, the system controller 101 counts the number of times the connection between the brush 705 and the commutator 704 is switched based on the electric current flowing through the coil 702 (winding wire) of the motor, and updates the count value in the RAM 104. The system controller 101 then updates the information regarding the residual amount of sheets based on the table T stored in the ROM 103 and the count value.

FIG. 7 is a control block diagram of the lifter control unit 113 of the present embodiment.

The lifter control unit 113 includes a motor drive unit 800, a current detection unit 801, a filter unit 802, a reference value setting unit 803, and a comparison unit 804.

The motor drive unit 800 includes an H-bridge circuit using a field effect transistor (FET), for example. In response to a command signal from the system controller 101, the motor drive unit 800 drives and stops the DC brush motor 600.

The current detection unit 801 detects a current value of a drive current flowing through the coil 702.

The filter unit 802 includes a band-pass filter, for example, but can include a filter such as a high-pass filter. The filter unit 802 extracts a signal in a predetermined frequency band from signals detected by the current detection unit 801. The predetermined frequency band includes a frequency of the spike current that increases due to the switching of the connection between the brush 705 and the commutator 704. That is, the filter unit 802 extracts a signal generated when the connection between the brash 705 and the commutator 704 is switched (spike current).

The comparison unit 804 includes a comparison unit such as a comparator. The comparison unit 804 compares a value output from the filter unit 802 with a reference value set as a threshold by the reference value setting unit 803.

When an absolute value of the value output from the filter unit 802 changes from a value smaller than the threshold set in the reference value setting unit 803 to a value greater than the threshold, the comparison unit 804 outputs a pulse signal to the system controller 101. Alternatively, the comparison unit 804 can output the pulse signal when the absolute value of the value output from the filter unit 802 changes from a value greater than the threshold set in the reference value setting unit 803 to a value smaller than the threshold.

By counting the pulse signal, the system controller 101 can determine the number of times the connection between the brush 705 and the commutator 704 is switched, that is, a rotation amount of the rotor of the DC brush motor 600.

FIG. 8 is a diagram illustrating current waveforms before and after processing by the filter unit 802 according to present embodiment is performed.

As illustrated in FIG. 8, a signal when the connection between the brush 705 and the commutator 704 is switched is extracted by the filter unit 802. Thus, the number of times the connection between the brush 705 and the commutator 704 is switched can be counted.

FIG. 9 is a flowchart indicating processing for detecting the residual amount of sheets according to the present embodiment. This flowchart is executed by the CPU 102 in the system controller 101.

When the power source of the image forming apparatus 100 is turned on, in step S901, the CPU 102 determines whether the sheet feed cassette open/close sensor 407 is ON.

In a case where the sheet feed cassette open/close sensor 407 is ON (YES in step S901), the sheet feed cassette 401 is in a closed state. On the contrary, in a case where the sheet feed cassette open/close sensor 407 is OFF (NO in step S901), the sheet feed cassette 401 is in an open state.

In the case where the sheet feed cassette open/close sensor 407 is OFF (NO in step S901), the CPU 102 stands by until the sheet feed cassette open/close sensor 407 is turned on.

In the case where the sheet feed cassette open/close sensor 407 is ON (YES in step S901), in step S902, the CPU 102 checks whether the sheet height sensor 406 is OFF.

In a case where the sheet height sensor 406 is ON in step S902 (NO in step S902), in step S908, the CPU 102 displays, on the operation unit 105, the residual amount of sheets based on the count value stored in the RAM 104.

In a case where the sheet height sensor 406 is OFF in step S902 (YES in step S902), in step S903, the CPU 102 resets the count value stored in the RAM 104.

In step S904, the CPU 102 starts driving of the DC brush motor 600. When the DC brush motor 600 starts to be driven, the CPU 102 starts counting pulses transmitted from the comparison unit 804 of the lifter control unit 113 at the timing when the connection between the brush 705 and the commutator 704 is switched, and stores a count value in the RAM 101.

The CPU 102 continues driving the DC brush motor 600 and counting the pulses until it is determined in step S905 that the sheet height sensor 406 is turned on.

When the sheet height sensor 406 is turned on (YES in step S905), in step S906, the CPU 102 stops driving of the DC brush motor 600.

Then, the CPU 102 also stops counting the pulses.

Thereafter, in step S907, the CPU 102 determines the residual amount of sheets based on the count value of the pulses stored in the RAM 104 and the table T stored in the ROM 103.

The CPU 102 then updates the residual amount of sheets displayed on the operation unit 105.

As described above, the residual amount of sheets can be detected with high accuracy by counting, during the period in which the DC brush motor 600 is driven, the number of times the connection between the brush 705 and the commutator 701 of the DC brush motor 600 is switched, based on the electric current flowing through the winding wire of the DC brush motor 600.

Other Embodiments

The present disclosure can also be implemented by processing including supplying a program that implements one or more functions of the embodiments described above to a system or a device via a network or a storage medium, and reading and executing the program by one or more processors in a computer of the system or the device. The present disclosure can also be implemented by a circuit (for example, an application specific integrated circuit (ASIC)) that implements one or more functions.

Furthermore, the present disclosure can be applied to a system including a plurality of devices or to an apparatus including one device.

The present disclosure is not limited to the embodiments described above, various modifications can be made based on the spirit of the present disclosure, and such modifications are not excluded from the scope of the present disclosure. That is, all configurations obtained by combining the embodiments described above and modifications thereof are also included in the present disclosure.

According to the present disclosure, it is possible to detect the residual amount of sheets with high accuracy.

While the present disclosure has been described with reference to embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2018-130467, filed Jul. 10, 2018, which is hereby incorporated by reference herein in its entirety. 

What is claimed is:
 1. An image forming apparatus comprising: a stacking unit including a stack tray on which a sheet is to be stacked; a conveyance unit configured to convey the sheet stacked on the stack tray; an image forming unit configured to form an image on the sheet conveyed by the conveyance unit; a direct current (DC) brush motor configured to lift and lower the stack tray in a vertical direction; a drive unit configured to drive the DC brush motor; a first detector configured to detect a drive current flowing through a winding of the DC brush motor; a first determiner configured to determine a rotation amount of a rotor of the DC brush motor based on the number of times an absolute value of a current value of the drive current detected by the first detector changes from a value smaller than a threshold to a value greater than the threshold; and a second determiner configured to determine a residual amount of sheets stacked on the stack tray based on the rotation amount determined by the first determiner.
 2. The image forming apparatus according to claim 1, further comprising an extraction unit configured to extract a signal in a predetermined frequency band from the drive current detected by the first detector, wherein the first determiner determines the rotation amount based on the signal after processing by the extraction unit is performed.
 3. The image forming apparatus according to claim 2, wherein the extraction unit includes a band-pass filter.
 4. The image forming apparatus according to claim 1, wherein the absolute value is increased when electrical connection between a commutator and a brush of the DC brush motor is switched.
 5. The image forming apparatus according to claim 1, wherein the stacking unit and the DC brush motor are connected by a gear.
 6. The image forming apparatus according to claim 5, wherein the gear includes a plurality of gears.
 7. The image forming apparatus according to claim 1, further comprising a memory configured to store data indicating a relationship between the rotation amount of the DC brush motor and the residual amount of sheets stacked on the stack tray, wherein the second determiner determines the residual amount of sheets stacked on the stack tray based on the data stored in the memory and the rotation amount determined by the first determiner.
 8. The image forming apparatus according to claim 1, wherein the stack tray moves to a first position when the stacking unit is pulled out from the image forming apparatus.
 9. The image forming apparatus according to claim 8, wherein the first position is a bottom position of the stack tray.
 10. The image forming apparatus according to claim 8, wherein, when the stacking unit is inserted into the image forming apparatus, the driving unit drives the DC brush motor such that the stack tray moves from the first position to a second position.
 11. The image forming apparatus according to claim 10, wherein the second position is a position where an uppermost sheet stacked on the stack tray is fed.
 12. The image forming apparatus according to claim 10, wherein the second determiner determines the residual amount of sheets stacked on the stack tray based on the rotation amount of the DC brush motor while the drive unit drives the DC brush motor to move the stack tray from the first position to the second position.
 13. The image forming apparatus according to claim 1, further comprising a second detector configured to detect an uppermost sheet stacked on the stack tray, wherein, when the stacking unit is inserted into the image forming apparatus, the drive unit drives the DC brush motor until the uppermost sheet is detected by the second detector.
 14. The image forming apparatus according to claim 13, wherein the second determiner determines the residual amount of sheets stacked on the stack tray based on the rotation amount of the DC brush motor while the drive unit drives the DC brush motor.
 15. An image forming apparatus comprising: a stacking unit including a stack tray on which a sheet is to be stacked; a conveyance unit configured to convey the sheet stacked on the stack tray; an image forming unit configured to form an image on the sheet conveyed by the conveyance unit; a DC brush motor configured to lift and lower the stack tray in a vertical direction; a drive unit configured to drive the DC brush motor; a detector configured to detect a drive current flowing through a winding of the DC brush motor; a first determiner configured to determine a rotation amount of a rotor of the DC brash motor based on the number of times an absolute value of a current value of the drive current detected by the detector changes from a value greater than a threshold to a value smaller than the threshold; and a second determiner configured to determine a residual amount of sheets stacked on the stack tray based on the rotation amount determined by the first determiner. 